1. Field of the Invention
This invention relates to a method and apparatus for scrambling and unscrambling of image data using an MPEG encoding digital video system.
2. Background Art
In previous methods for scrambling of MPEG encoded images, the MPEG encoded video data are scrambled by disassembling the data into bit units and reassembling the disassembled data using an algorithm which has no relation to the MPEG encoded images itself. Therefore, the image data scrambled by this method becomes completely non viewable.
However, the MPEG decoding system does not recognize the image data scrambled by the above method as video data which are encoded by MPEG standards, and the risk arises that the MPEG decoder will malfunction or will be broken down when the scrambled data are input.
Furthermore, because the image data scrambled by the above method is completely non viewable before the unscrambling of the data, even users having permission to unscramble the scrambled data cannot recognize whether the receiving data are the scrambled video data or mere noise. Therefore, unless the sender of the scrambled data informs the receiver that scrambled data are being transmitted, the receiver cannot unscramble the transmitted data to see the original image data.
In order to solve the above problems, in the method for disassembling video data into bit units and reassembling using an algorithm having no relation to the MPEG encoded video data, it is effective to leave part of the image data stream unscrambled, while scrambling the remaining part. In this case, since the partly scrambled data complies with the MPEG standards, a malfunction or the brake-down of the decoding system can be avoided; furthermore, the receiver can easily recognize that the receiving data is scrambled image data.
However, because the above method leaves part of the image data in a visible state, it is far from a complete scrambling of the image data. Additionally, the selection of the part to be visible should be entrusted to the copyright holder of the image data to be scrambled.
It is therefore an object of the present invention to scramble an MPEG encoded image stream so that the scrambled data stream will comply with MPEG standards and an MPEG decoder will not malfunction or be broken down when scrambled data are input. It is another object of the present invention to scramble an MPEG encoded image stream so that user receiving the scrambled data can distinguish the scrambled data from mere noise. It is further another object of the present invention to enable the scrambling and unscrambling with simple circuits and at a low cost.
In order to accomplish the above objects, the image scrambling apparatus of the present invention comprises:
a first dividing decoder for dividing an MPEG encoded image data stream into a plurality of data segments;
at least one arrangement table recording arrangement information to be used for arranging the data segments;
an arrangement circuit for arranging the data segments output from the first dividing decoder in accordance with the information recorded in the arrangement table to output a scrambled image data stream;
a second dividing decoder for dividing the scrambled image data stream into a plurality of data segments;
at least one rearrangement table recording rearrangement information to be used for rearranging the data segments output from the second dividing decoder; and
a rearrangement circuit for rearranging the data segments output from the second dividing decoder in accordance with the rearrangement information recorded in the rearrangement table.
The first dividing decoder, the arrangement table, and the arrangement circuit may be included in a transmitter, and the second dividing decoder, the rearrangement table, and the rearrangement circuit may be included in a receiver. However, the present invention is not limited to this construction, and all features may be contained in an apparatus or a system.
According to this scrambling apparatus, the scrambled image data consists of data segments each of which complies with MPEG standards, and the scrambled imaged data itself also complies with the MPEG standards. Therefore, an MPEG decoder receiving the scrambled data will not malfunction or be broken down.
Furthermore, although the scrambled image data is non viewable, because the image replayed from the scrambled image data exhibits a characteristic pattern which is different from that replayed from mere noise, users can easily distinguish the scrambled image data from mere noise. Additionally, digital processing for dividing and arranging the image data stream is simple, and it is possible to simplify the circuit for the scrambling and unscrambling.
In the scrambling apparatus of the present invention, the first and second dividing decoder may divide the data stream into macro blocks or slices as the data segments. As shown in FIG. 7, an MPEG encoded image data stream consists of a plurality of slices, and each slice consists of a plurality of macro blocks. In the general MPEG standards, each macro block consists of 16xc3x9716 pixels; however, the macro block to be used in the present invention is not limited to this size.
By dividing an MPEG encoded image data stream into a plurality of macro blocks and arranging the macro blocks so that each macro block is positioned at a position different from its original position in the data stream, it becomes impossible for an MPEG decoder to replay the image, even though the MPEG decoder will not malfunction and will not be broken down. The same effects can be obtained when dividing the image data stream into slices.
The scrambling apparatus of the present invention may comprise a table transmitter and a table receiver. The table transmitter transmits the arrangement information recorded in the arrangement table to the table receiver, and the table receiver calculates the rearrangement information from the arrangement information and records the rearrangement information in the rearrangement table. In this case, it is easy to use various arrangement tables without complicated operations at the receiver side.
The scrambling apparatus may include a plurality of arrangement tables respectively recording various arrangement information different from each other and having table numbers different from each other. In this case, the table transmitter transmits to the table receiver only the table number corresponding to the arrangement table to be used. Next, the table receiver calculates the rearrangement information from the arrangement information recorded in the arrangement table corresponding to the received table number, and records the rearrangement information in the rearrangement table.
Another aspect of the present invention is an image scrambling method for scrambling an MPEG encoded image data stream, and this method comprises the steps of:
providing an arrangement table recording arrangement information to be used;
dividing the MPEG encoded image data stream into a plurality of data segments; and
arranging the data segments in accordance with the information recorded in the arrangement table to output a scrambled image data stream.
Another aspect of the present invention is an image unscrambling method for unscrambling an image data stream scrambled by the above scrambling method, and this method comprises the steps of:
dividing the scrambled image data stream into a plurality of data segments;
providing a rearrangement table recording rearrangement information to be used for rearranging the data segments; and
rearranging the data segments in accordance with the information recorded in the rearrangement table to output an unscrambled image data stream.
Another aspect of the present invention is a computer-readable medium containing computer-readable instructions, and this medium comprises:
means for causing a computer to provide an arrangement table recording arrangement information to be used;
means for causing a computer to divide an MPEG encoded image data stream into a plurality of data segments; and
means for causing a computer to arrange the data segments in accordance with the arrangement information recorded in the arrangement table to output a scrambled image data stream.
Another aspect of the present invention is a computer-readable medium containing computer-readable instructions, and this medium comprises:
means for causing a computer to divide a scrambled image data stream into a plurality of data segments;
means for causing a computer to provide a rearrangement table recording rearrangement information to be used for rearranging the data segments; and
means for causing a computer to rearrange the data segments in accordance with the rearrangement information recorded in the rearrangement table to output an unscrambled image data stream.
Each of the above aspects of the invention can accomplish the objects as described.